"We ask our allies and partners to join our economic pressure campaign against Iran's regime," Pompeo wrote on Twitter ahead of Thursday's scheduled talks with the European Union's foreign policy coordinator, Federica Mogherini. "We must cut off all funding the regime uses to fund terrorism & proxy wars. There's no telling when Iran may try to foment terrorism, violence & instability in one of our countries next."

Pompeo appended a map claiming that Iran had at least indirect involvement in at least 11 terrorist attacks in Europe since 1979. However, he did not specify precisely which attacks it referred to, nor did he make any case for why or how Iran had been involved.

'In blatant violation'

Earlier this week, Pompeo asked NATO members to join the US-led campaign to put economic pressure on Iran. The United States began earnest efforts to isolate Iran economically in May, after President Donald Trump withdrew from a landmark nuclear deal that the administration of his predecessor, Barack Obama, and the governments of five other countries had spent years negotiating. The multinational deal lifted many sanctions imposed for years on Iran in return for the country's voluntary curbing of its nuclear program.

"Iran continues to send weapons across the Middle East, in blatant violation of UN Security Council resolutions," Pompeo also wrote on Twitter on Thursday. "Iran's regime wants to start trouble wherever it can. It's our responsibility to stop it."

Since Trump's decision to withdraw from the agreement, EU member states have scrambled to ensure that Iran gets enough economic benefits to persuade it to maintain the nuclear curbs required by the deal. But, so far, it has proven difficult to offset the impact of US sanctions, with EU firms reluctant to risk far-reaching financial penalties for doing business in Iran. Additionally, the United States has ordered countries to halt imports of Iranian oil by November 4 or face US financial measures — with no exemptions.

"I would say there might be an escalation between us and the Iranians," Trump, who was also in Brussels for this week's NATO summit, told reporters earlier on Thursday. However, he added, the country had begun "treating us with much more respect right now than they did in the past."